package com.cr4y0n.hot100;

/**
 * @author cr4y0n
 * <a href="https://leetcode.cn/problems/reverse-linked-list/description/?envType=study-plan-v2&envId=top-100-liked">反转链表</a>
 * 给你单链表的头节点 head ，请你反转链表，并返回反转后的链表。
 * 示例 1：
 * 输入：head = [1,2,3,4,5]
 * 输出：[5,4,3,2,1]
 * 示例 2：
 * 输入：head = [1,2]
 * 输出：[2,1]
 * 示例 3：
 * 输入：head = []
 * 输出：[]
 */
public class _206_ReverseLinkedList {

    public static class ListNode {
        int val;
        ListNode next;

        ListNode() {
        }

        ListNode(int val) {
            this.val = val;
        }

        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }

    static class Solution {
        public ListNode reverseList(ListNode head) {
            ListNode pre = null;
            ListNode next = null;
            while (head != null) {
                next = head.next;
                head.next = pre;
                pre = head;
                head = next;
            }
            return pre;
        }
    }
}
